I just got my first jeep. It's a 91 Cherokee with a 4.0 with 211K miles on it. When I start it cold it has 60 PSI oil pressure after it's warm it has 20 PSI oil pressure then stays there the whole time I'm driving stopped or moving. This seams low to me. Is this normal?

 

200k is alot of miles. its abit low but 20 psi will work. if you are overly concerned you could throw a new oil pump in it and roll some new bearings in it in a day.

 

do you have a stock oil pressure gauge or an after market mechanical/electronic gauge?

 

the stock gauge is not the most accurate thing in the world. i picked up an after market gauge to check mine, ended up permanently mounting it too. it reads about 45-50 psi at cruising speeds and climbs to just below 60 for higher RPM shifts. and only drops down to 20 psi during medium-long idles (about 2 minutes and up)

 

Stock gauge. I have a local shop that will replace the rod, main bearings, oil pump and timing chain for 1200 bucks. If I go this route should I use high volume pump or a stock pump?

 

those readings sound pretty normal

 

One thing I have thought about is maybe the oil pressure sending unit is not working right.

 

that is a lot cheaper to fix, but those numbers don't sound out of the ordinary.

 

that could be it, test it with a meter to be sure. and DO NOT go high volume pump, go with a stock Melling. and put some thought into it before you decide to have the main and rod bearings replaced. if the shop pulls the bearings and replaces them without measuring the crank it could lead to more issues down the road with excessive oil clearance, due to not having the crank polished or ground to the correct size, thus leading to slap in the rods and possible rotating assembly failure down the line. and for the amount of money i assume your willing to spend you should look into a full rebuild...especially because the $1200 you would pay the shop to do your bearings, pump and timing would almost pay for a rebuild give or take a few $100...just my 2 cents...

 

My jeep was around 45 at start up and then lowered to around 20 on stock gauge before the rearend went out. But it never did go below 20